Lithographic printing presses have plural rollers that are used in applying ink to paper. The paper passes between a blanket cylinder and an impression cylinder, wherein the blanket cylinder forms an impression of wet ink on the paper. The blanket cylinder is inked by a plate cylinder and the plate cylinder is inked by a set of inking rollers. Multicolor presses require for each color a set of inking rollers, a blanket cylinder, an impression cylinder, and a plate cylinder.
A chemically treated printing plate that has hydrophilic (or water-loving) areas and separate oleophilic (or oil-loving) areas is attached to the plate cylinder for printing. These areas are arranged in a pattern to produce the desired printed image on the paper. The ink is attracted to the oleophilic areas and repelled from the hydrophilic areas. Thus, as the printing plate rotates, the inking rollers apply ink to the oleophilic areas on the printing plate.
Ink is provided by the manufacturer in a viscous form. It must be applied to the printing plate together with the proper amount of a fountain solution. The fountain solution is made of primarily water into which is mixed other chemicals. If there is too much fountain solution being applied to the printing plate, the print on the paper will lose color and fade. If there is an insufficient amount of fountain solution being applied to the printing plate, the printing plate becomes dirty, reducing the clarity of the print and causing print to appear in nonprint areas.
In the prior art, there are two kinds of dampening systems for applying the fountain solution to the printing plate. One type of dampening system applies the fountain solution directly to the printing plate with a separate set of dampening rollers. This type of dampening system can cause streaking in the printed areas because the fountain solution is unable to be evenly distributed on the printing plate. This type of system is sometimes motor driven.
The other type of dampening system applies the fountain solution to the printing plate indirectly through the ink. The ink on the inking rollers is dampened with the fountain solution before it is applied to the printing plate. This type of system uses a ducting roller to intermittently contact and apply the fountain solution to an inking roller. The ducting roller reciprocates in and out from the inking roller to provide intermittent contact. The ducting roller generally has a metal surface, being either copper-plated or chrome-plated. The ducting roller is driven by a gear coupled to the inking roller. While the ducting roller prior art dampening system does apply the fountain solution in an even distribution to the printing plate, it is inadequate because the amount of fountain solution that is mixed with the ink cannot be controlled with sufficient precision. This mixture, which is applied to the printing plate, contains either too much or too little fountain solution. It is desirable to provide an automatic dampening system that allows accurate application (or metering) of the fountain solution into the ink.